Puch Maxi

I can’t seem to figure out why my moped doesn’t pull gas-air into piston chamber. I bought a carb kit, replaced all pieces, changed gasket on pistol and intake amd still no gas to piston chamber. I have spark but no gas. Spark plug is dry. Not sure what is going on. It worked two years ago, I left it through one winter and now I can’t get it to start. Could my carburetor be bad or are my piston rings the issue. I have compression just no gas getting to chamber.

It must be something simple, has anyone had something similar.

Thanks

Re: Puch Maxi

Wesley Ambrosini /

Float height in the carb

Bad flow through the petcock

Re: Puch Maxi

Try again. Check jet

Re: Puch Maxi

Clean jets, Is there a test I could do. I am running out of ideas. Thanks

Re: Puch Maxi

Lots of gas in Float area. Not sure where I should put mixture adjustment on carb. I gave it 3.5 counter clockwise turns.

Also choke is on and still no gas getting to chamber.

Re: Puch Maxi

Put your hand over the carb intake and try starting .

Insure that the exhaust is clear .

Re: Puch Maxi

So did some further tests,

Compression: Good

Fuel flow: Good

Jets: Clean and Good

I put some fuel in cylinder, kicked it over and got a Backfire. So I know the problem is no fuel to cylinder. Will keep trying but I am losing my patients. Grrrrrrrr

Re: Puch Maxi

> Jim Stewart Wrote:

> -------------------------------------------------------

> So did some further tests,

> Compression: Good

>

What is good ?

And , have you done as suggested ?

A backfire would have me checking timing , to be sure .

Re: Puch Maxi

For compression, i plugged the hole with a tight rubber stopper, cranked the engine and it blew the rubber from the cylinder real hard, can’t find the stopper anymore.

As for timing, i would still get gas in the cylinder. I had to manually put a bit in.

Re: Puch Maxi

For timing, do this:

https://www.mopedarmy.com/wiki/Puch_timing

For compression, use this:

E7A4E443-5E8C-452A-AA8D-871C8882FC02.jpeg

Re: Puch Maxi

Overpriced Parts /

There is a vent hole on bing carbs that if blocked the bowl will not fill

Re: Puch Maxi

^ yep

Re: Puch Maxi

The bowl is filling and full, not issue. I have a feeling gas may be too rich. Will try pure gas to see if I have too much mixture and too thick to get through jet in bing

Re: Puch Maxi

Timing or not, still not flooding spark plug. That’s the main issue , thanks

Re: Puch Maxi

When the piston goes up, it should suck fuel/air mix through the carburetor into the case. When the piston goes down, it pushes the fuel mix into the cylinder. This vacuum/pressure cycle only works properly if you have no air leaks. You may have a big one. If you are sucking air through a crank seal, or base gasket, or intake leak, then it isn’t sucking fuel mix through the carburetor.

Re: Puch Maxi

Moped Lar (OFMC) /

Air leaks suck ;-)

Re: Puch Maxi

Dirty30 Dillon /

> Jim Stewart Wrote:

> -------------------------------------------------------

> The bowl is filling and full, not issue. I have a feeling gas may be too

> rich. Will try pure gas to see if I have too much mixture and too thick

> to get through jet in bing

This would require you to have made a MAJOR miscalculation.

I am guessing that you have an airleak which is causing your issues.

It could also be stuck rings

Re: Puch Maxi

I took the head off and checked all gaskets. All were good. The no leaks on cylinder.

Question. the intake valve that opens when kicking the engine over, does that have anything to do with leak. It makes sense that it open so the air expels when turning the piston over.

Is there any tests I can perform to diagnose if a leak exists. Would the exhaust gasket cause an issue. I know the intake for carb would. Other than these, not sure what else

Thanks

Re: Puch Maxi

Dirty30 Dillon /

Visually inspecting gaskets and seals is not a viable way of determining whether they are leaking or not.

THAT SAID, if you have a decompression valve head Maxi (which the vast majority of Maxi's in the States ARE NOT), than I would consider that a prime suspect. Either mis-adjusted or there is carbon in the valve holding it open.

Re: Puch Maxi

> Jim Stewart Wrote:

> -------------------------------------------------------

> Question. the intake valve that opens when kicking the engine over, does

> that have anything to do with leak. It makes sense that it open so the

> air expels when turning the piston over.

>

Explain this?

Re: Puch Maxi

When I pull the starter, it opens a valve on the bottom of the cylinder to let the compression come out. I guess this is so the gas can come into cylinder. Once it fire, we release and the engine runs. Thats all I can see it for.

Re: Puch Maxi

I will check it again but this moped hasn’t ran in two years. When I did get it working, it only ran for short period. I was still in the rebuild stage.

Re: Puch Maxi

> Jim Stewart Wrote:

> -------------------------------------------------------

> When I pull the starter, it opens a valve on the bottom of the cylinder

> to let the compression come out. I guess this is so the gas can come

> into cylinder. Once it fire, we release and the engine runs. Thats all I

> can see it for.

Maybe your piston is upside down.

Re: Puch Maxi

If your decompression valve is leaking, That’s your air leak, and you won’t get fuel.

Re: Puch Maxi

thanks, will check the valve seal. would you know what the compression PSI might be.

Re: Puch Maxi

I just did a top end rebuild and with no carb on the intake, and spun with a cordless drill, I got 130 PSI. Make sure you check with the throttle wide open or the carb removed.

Re: Puch Maxi

> Jim Stewart Wrote:

> -------------------------------------------------------

> thanks, will check the valve seal. would you know what the compression

> PSI might be.

110-140 PSI is typical

Re: Puch Maxi

Ok, replaced all gaskets and still no air/gas getting into cylinder. Plug is fry as a bone. Took engine apart again and found gas in cylinder but not getting into combustion chamber.

When I put my finger over intake, there is suction just not sure how much there should be.

I have two more options but before, wanted to ask. The option are a new Bing and/or piston rings.

Any other suggestion would be greatly appreciated. Thanks

Re: Puch Maxi

How many pounds compression ?

I can make a rubber plug disappear just by my poor lung pressure .

Fuel in the case and not the chamber indicates a lack of compression or too slow of initial RPMs .

Are you trying to start it with a drill ?

Re: Puch Maxi

Pushrod Fifty /

If you feel suction you have compression. Gas can be hard to see on a clean plug. You could have a clogged exhaust. Pull the baffle out and see if it starts, or loosen the nuts holding the exhaust pipe to try. If it fires, remove and clean the inside.

Any gasketed parts that you remove will need new gaskets, the gasket wont work again.

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